Method for producing capped 3-hydroxycarboxylic acids and their salts and esters

1. A method for producing capped 3-hydroxybutyric acid or s salts or esters,

wherein at least one compound of the general formula (I)

CH 3 —CH(OH)—CH 2 —C(O)OR 1   (I)

wherein in the general formula (I) the radical R 1 represents hydrogen, methyl or ethyl,

is reacted with at least one carboxylic acid anhydride of the general formula (II)

R 2 —C(O)—O—C(O)—R 3   (II)

wherein in the general formula (II) the radicals R 2 and R 3 , each independently of one another, represent a linear or branched, saturated or mono- or polyunsaturated C 3 -C 21 -alkyl,

wherein the reaction of the at least one compound of the general formula (I) with the at least one carboxylic acid anhydride of the general formula (II) is carried out in the absence of any solvents,

so that, as reaction product, there is obtained one or more capped 3-hydroxybutyric acids or their salts or esters of the general formula (III)

CH 3 —CH[O—C(O)R 5 ]—CH 2 —C(O)OR 4   (III)

wherein in the general formula (III) the radical R 4 represents methyl, ethyl or a metal ion and the radical R 5 represents a radical R 2 or R 3 each having the meaning defined hereinabove.

2. The method according to claim 1 ,

wherein the reaction of the at least one compound of the general formula (I) with the at least one carboxylic acid anhydride of the general formula (II) is followed by hydrolysis in the case that R 1 represents hydrogen.

3. The method according to claim 2 ,

wherein the hydrolysis is carried out under acidic or basic conditions.

4. The method according to claim 1 ,

wherein the compound of general formula (I) is used in racemic form or in the form of the (R)-enantiomer.

5. The method according to claim 1 ,

wherein, as a compound of the general formula (I), 3-hydroxybutyric acid ethyl ester of the formula CH 3 —CH(OH)—CH 2 —C(O)OC 2 H 5 is used.

6. The method according to claim 1 ,

wherein, as a carboxylic acid anhydride of the general formula (II), a compound in which the radicals R 2 and R 3 are identical is used.

7. The method according to claim 1 ,

wherein, as a carboxylic acid anhydride of the general formula (II), a compound in which the radicals R 2 and R 3 are different from one another is used.

8. The method according to claim 1 ,

wherein the reaction of the at least one compound of the general formula (I) with the at least one carboxylic acid anhydride of the general formula (II) is carried out at temperatures in the range of from 60 to 150° C.; and

wherein the reaction of the at least one compound of the general formula (I) with the at least one carboxylic acid anhydride of the general formula (II) is carried out at a pressure in the range of from 0.0001 bar to 10 bar.

9. The method according to claim 1 ,

wherein during the reaction of the at least one compound of the general formula (I) with the at least one carboxylic acid anhydride of the general formula (II), a compound of the general formula (IV)

R 5 —C(O)—OH  (IV)

is formed simultaneously, wherein the radical R 5 has the meaning defined hereinabove;

wherein the compound of the general formula (IV) is removed during or after the reaction has taken place.

10. The method according to claim 1 ,

wherein the reaction of the at least one compound of the general formula (I) with the at least one carboxylic acid anhydride of the general formula (II) is followed by purification;

wherein any starting compounds and reaction by-products still present are distilled off.

11. The method according to claim 1 ,

wherein, as a reaction product, one or more capped (blocked) 3-hydroxybutyric acid salts and/or esters of the general formula (III)

CH 3 —CH[O—C(O)R 5 ]CH 2 —C(O)OR 4   (III)

is formed,

wherein in the general formula (III)

the radical R 4 represents methyl or ethyl,

the radical R 5 represents a linear or branched, saturated or mono- or polyunsaturated C 3 -C 21 -alkyl.

12. The method according to claim 1 ,

wherein, as a reaction product, one or more capped (blocked) 3-hydroxybutyric acid salts and/or esters of the general formula (III)

CH 3 —CH[O—C(O)R 5 ]—CH 2 —C(O)OR 4   (III)

is formed,

wherein in the general formula (III)

the radical R 4 represents ethyl,

the radical R 5 represents a linear or branched, saturated or mono- or polyunsaturated C 3 -C 21 -alkyl.